Check this out - a Mosin Nagant styled bolt in 12 gauge! I say "styled" because the description indicates it used the Mosin design for some signalling/launching device but doesn't give particulars.

I suppose the question is would a Mosin receiver have the strength to hanlde 12GFH? Since the 7.62x54R is published to pressures of 50,000 CUP I would think it is, considering the other bolt actions that have been converted?

This bolt was used in a European mounted type device that used a 12 Ga. shotshell to propel weather balloons. Although the device uses a Mosin Nagant style bolt, it is not related in any way to the standard Mosin Nagant series rifles. Quantities are very limited.

Matthew in Oregon got the 12GA FH Savage.
He is now in the recoil club.

Here is picture of the 12ga belted cases I made to
test a few loads in. I made it from 55cal belted
Boys case. I reduced belt diameter a little and left
the base the same, which is 12ga size.In picture
first is 55cal, second expanded to .620", third
expanded to .660"(16ga), then two 12 ga ones.
Next is our 12GA FH, and then a 12ga 3.5"
plastic case.A little work in long 12ga FH chamber
with a tool for belt step and it chambers. Ed

Here is a picture of US-S brass slug after going through
3 foot of wood slabs in a bundle. It has shed its plastic
base and it went through straight without tumbling.
This one is 570 gr fired at 2200 in RMC case, from NEF.
Also in picture is one with white sabot petals off, as it
would be in flight, before hitting target.Ed

That's impressive! Not much expansion, although as I type this I suppose that doesn't NEED much expansion, does it?

A question for you Ed,

I'm building my cases and as I've said I'm going with inserts to use with shotgun primers. From what I've been reading it seems as if the 7383 powder is a good starting point. Would you use 10g of starter powder with 7383?

Also a question about inserts:

With shotgun primers, do you need the insert to cover the inside tip of the shotgun primer to make a flash hole like the BMG primers use? Or is it OK to complete drill out and use like a normal shotgun primer? The reason I ask is I don't know how the pressure will be affected if the insert is all-open vs. flash hole

I have cases with inserts drilled all the way through just like regular
12ga cases and like RMC brass cases.I drill all the way through and
thread it and put in insert and drill it through. The shotgun primer
battery cup has its own flashhole. You don't need any starter powder
with surplus 7383. Or RE17 which is better yet, as it is a little faster.
On all slug/sabots must use a good proper roll crimp for dependable
ignition.

Could you show pictures of your case building process.
And do a description of it for the folks.

4bore work. Working on design of firing pin,
and waiting for parts now. Problem is getting
real small parts without CNC for bushed
firing pin with rebound spring. But it takes
time.

We will have swaged lead slugs
in a little while as my barrel is smooth. They
will be 1600gr hollowbase, when done,
a hundred of them at least.
Got wads and cards, shown in the picture with 4bore
cases and slugs. And my 2bore case for comparison
Also 12ga wads for comparison..Ed

Our cartridge work and experimenting got a nice
write up in # 470 Nov/Dec International Ammunition
Journal. Page 10-11 by Zach Weighman, a
cartridge collector and gun nut friend.

Got a guy just figured out BMG case rim, and for a rim
puts on 12ga high base cup from a plastic case. He turns
base/rim of bmg case about .008" and use JB Kwik to hold
it on. Pushes it on with press. He removes base cup with
heat gun from plastic cases,

He is using RE17, so shotgun primers will work, and he
puts bushing in case for primer. Has bushing reamed so
the primer pocket protrusion on the base cup goes up inside
tight, as he pushes on the base cup. It'll fire ok and to size it
do like I do, I push case into open top die, and push it
back out from the top with a rod and hammer. That
way the rim don't get bent up. He says it saves a lot of
time not having to make rim pieces.

Here is a picture of a BPI sabot with a BPI Flexseal I
use on to it in place of the original cushion seal.
I also cut shallow slots in the outside at the bottom
of the petals. Sabot opens much quicker and seems
along with BPGS seals under it to work ok without
damage, giving high velocities. In pic on left is regular
BPI sabot, behind is one I put a cushion on from a
Brenekke KO slug, and in front the one with Flexseal on.
The slug in it is one a guy casts at 440 gr and .504"
diameter, and works ok.

New info on my 499HE, from now on we will make cases
out of 450 #2 brass, as Jamisons has 3-4000 cases,
and it seems no one has the 475 #2 we used first.
Only slight case dimension change is the base .012"
smaller, all else is the same. I'm getting reamers redone
and will be able to use in couple weeks. Case will still have
plenty of taper to extract easy in singles, doubles,
falling blocks.etc.

And speaking of falling blocks I found one, and put my 585HE
in it, and it is big enough and has enough clearance to be used
for a 577NE, 600NE, long 20ga, my long 16ga FH,
the 700H, the 700HE. Cost no more than Ruger, with barrel
figured in. Will have pics
and info soon. Ed

Here is picture, Falling Block I found that I put
my 585HE in. It didn't need any work on the
feed trough to feed. 585 case shown in it.
In fact the trough is big enough
and the action big enough for 600NE, 3.5" 20ga
brass, 3.5" 16ga FH brass, my 700 HE long case.
I reworked a NEF stock to it, as I'm not
a stockmaker.Nice action.2nd picture is
of the 16GA FH in the feed trough.Ed

Here is picture of the FBW falling block with my
700HE long case in it.This falling block is 1.5"
wide, with a 1.125" wide breach block.
The sides are .187" thick next to breach block.
This compares to about .165" say for a Browning
B-87, Win copy. The feed trough would work with
12ga size rim if some work was done on the top
of the hammer. This has a barrel thread length of
1.005", thread diameter of 1.125" for good
strength. Ed